Bimetal element



May 29, 1928.

WITNESSES:

1,671,490 H. SCOTT BIMETAL ELEMENT Filed Dec. 27, 1926 INVENTOR I Hon/0rd scoff.

. BY v a fATTONEY Patented May 29,

UNITED S TATES PATENT-OFFICE,

HOWARD SCOTT, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR '10 WESTINGNOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OFv PENNSYLVANIA.

'nmErAI. niEmEN'r.

Application filed December 27, 1926. Serial 110. 157,321.

My invention relates to thermostatic devices and partigularly to bimetallic elements therefor. t a I &

An object of my invention is to provide a l bimetallic element for a thermostatic device that shall have uniform-and high temperature deflection characteristics over a predetermined range of temperature.

Another object of my invention is to provide a bimetallic element for a thermostatic device that shall have temperature deflection characteristics from low temperatures to above 300 C. similar to that of a bimetal having brass for the expanding element, but

i having greater strength at high temperatures than a brass bimetallic element.

In practicing my invention 1 provide a bimetallic element for a thermostatic device in which the metalhaving the low temperature coeflicient of expansion is an alloy of nickel and iron and the cooperating metal therefor is an alloy of manganese, nickel and iron. The manganese-nickel-iron alloy has a high temperature coeflicient of expansion that is uniform over a relatively wide range of temperatures, say from -100 C. to +500 C.

A bimetal composed of two metallic alloys, of which is nickel steel and the other which is manganese, nickel and iron, is very sensitive to temperature changes, particularly at temperatures to which bimetal is ordinarily subjected.

In the single sheet of drawings, the temperature expansion characteristics of a-ferrous alloy containing manganese and nickel and-a second ferrous alloy containing nickel are illustrated diagrammatically by means of curves. The difference in expansion between these alloys, which is a measure of the deflection at any temperature that can be obtained when these alloys are joined into a bimetallic strip, is also plotted.

In the drawings the ordinates of the curves 3 represent deflection in thousandths per unit length per degree centigrade and the abscissae represent temperature indegrees centigrade.

Curve 11 represents the temperature expansion characteristics of a ferrous alloycontaining approximately equal parts\ of manganese and nickel in substantial quantities. Curve 12' represents the temperature expansion characteristic of a relatively low expansion ferrous alloy that contains ap'' proximately 38% nickel and curve 13 represents the temperature deflection characteristic of a bimetal composed of the alloys represented by the curves 11 and 12. The ordinates of curve 13 are obtained by subtracting the ordinates of curve 12 from the ordinates of curve 13.

While I have designated a ferrous alloy containing 38% nickel as the low expansion element of my improved bimetallic element, I do not wish to be limited to the use of this alloy as other alloys having a low temperature coeflicient of expansion may' be employed. When using a ferrous alloy containing nickel, the nickel content may be as high as 45% if so desired.

It is to be noted that the alloy represented by the curve 11 is 'concave' upwards from 150 to approximately 75 C. and from -75 C. to +450 C. the curve is substantially a straight line, the regularity of which indicates that the alloy composed of man anese, nickel and iron expandssubstantifily uniformly over the temperature range from 75 C. to +450 C.

The curve 12 represents approximately a 38% nickel iron alloy that cooperates with the alloy represented by curve 11 and it is to be noted that the expansion characteristic of the nickel iron alloy is substantially uniform between 100 C. to substantially +250 C.

- The temperature expansion characteristics of a bimetal composed of the alloys representedby the curves 11 and 12 is particularly illustrated by curve 13. It is to.be noted that bimetal composed of these alloys has substantially uniform deflection from C. to substantially .+250' C. At temperatures higher than 300 C. the bimetal deflects at a lower rate than it doesbetween l00 G. and 300 C. and the curve approaches the horizontal, indicating that the deflection descreases with further increases of temperature.

The temperature range for a uniform deflection coeflicient characteristic of the temperature deflection coeflicient between 0 C. and 250 C. can be'extended to temperatures ihigher than 250 C. Thus, a bimetal composed of the alloy of curve 11 and an alloy having a higher nickel content than the alloy of curve 12 will have a straight line deflection characteristic from -100 C. to a temperature higher than +300 (1., depending on the increase in nickel of alloy corresponding to curve 12.

f pure iron is heated gradually to high temperatures, and the expansion thereof is recorded, it'will be found that, it ex ands quite uniformlyup to about 900 at which temperature, the metal undergoes a. change in crystalline structure known as a transformation point of the iron. Up to 900 C, thercrystalline structure of the iron is commonly known as Alpha iron. From 900 C. to 1400 C. pure iron expands liniformly but at a much higher rate than it does at temperatures below 900 (1' The increased coeificient of expansion between the teinperatures 900 C. and 1400 C. is attributable to a new crystalline structure coim r monly kno'wn as Gamma iron or Austenite.

The temperature coefiicient of expansion of Austenitic iron is substantially 20x10 centimeters per C. Above 1400 ,C. the

structure of'the ironchanges to that known as Delta iron.

I have found that by adding an appreciable amount of manganese to pure iron the temperature expansion characteristic of Austenitic iron may be obtained at low temperatures, say between ,100 C. and

+400 C. An addition of nickel, or "some other alloying element that has the same effect, to the alloy, the characteristics of which are illustrated by curve 11, is used to raise the Gamma to Delta transformation above the proposed range of temperatures. Since the manganese is not as expensive as nickel it is desirable to use manganese as the predominatin alloyin element so ,far

I as other characterlstics of t e alloy will permit.

Manganese in sufficient quantity. lowers the temperature of the irreversible transformation of Alpha to Gamma to temperatures below normal, but also brings the other irreversible' transformation of iron, Gamma and "Delta, within the desired working range. The fiinction of the nickel is, to raise this latter transformation above the working range. Thus with 10% nickel, the high expansion characteristic of Austeniteor Gamma iron is available over a temperature range between at: least '-100 C..to +400 C. Curve 11 gives the expansion characterist'icof such an alloy. g

It is desirable that the manganese content A 'plus two and one half times the nickel content shall not be less than 30%. The

amounts of, ni kel and manganese may be present larger quantities provided the eneral temperature characteristics of the a loy-rep'resented by the curve 11 do not depart materially therefrom' I have found that agferrous' alloy, of the character beige that referred to, containing 10% manganese, and 10% nickel is particularly; responsive to changes in temperature and has a uniform temperature expansion characteristic.

l have provided a bimetallic element that is composed of ferrous alloys, the high expansion member of which is a manganesenickel-ironalloy and the other of which is a nickel iron alloy. The bimetal has a uniform temperature expansion characteristic from temperatures below zero degrees C. to above 250 C. The temperature expansion range of this bimetal may be varied by increasing or decreasing the nickel content of the nickel-iron alloy. The temperature expansion characteristics of the bimetal may also be varied in accordance with the application to which it is to be adapted by varying either or both the manganese and nickel content in the iron-nickel-manganese and the nickel content in the iron-nickel alloy.

Various modifications may be made in the device embodying my in'y ention withoutde 1 parting from the spirit and the scope thereof. I desire therefore that only such limitations shall be placed thereon as are imposed by the prior'art and the appendedclaims.

I claim as my invention:

-1. A thermostatic element comprising a pair of metallic elements having different temperature coelficients of expansion, one of said elements being a ferrous alloy rontaih- I ing substantially 15% manganese, and the other of said elements being a nlckel-iron alloy.

2. A thermostatic element comprising a pair 'of metallic elements having different temperature coelficientsof expansion, one of said elements being a ferrous alloy containing substantially equal parts of nickel and manganese, and the other-of 'said elements being a nickel-iron alloy.

3. A thermostatic element comprising a pair of metallic elements having different -ing nickel and manganese, the. manganese,

content beingnot less than 8%, and the other of said. elements a nickel-iron alloy.

5. A thermostatic element comprising two cooperatirg ature coe ients of expansion, one of said elements being a ferrous alloy containing metals having difl'erent tempernickel and manganese, the manganese content being not more than 15% of the alloy aggregate, and the other of saitl elements being a nickel-iron alloy.

6. A thermostatic element comprising two cooperating metals having difierent temper ature coeflicients of expansion, one of said. elements being a ferrous alloycontaining substantially 10% nickel and 10% manganese, and the other. of said elements being a nickel-iron alloy.

7. A thermostatic element comprising two cooperating metals having different temperature coeflicients of expansion, one of said elements'being a ferrous alloy containing nickel aml manganese, and the other of said elements being a nickel iron alloy.

8. A thermostatic element comprising two cooperating metals having diflerent temperature coeflicientsof expansion, one of said elements being a ferrous alloy containin nickel and manganese, and the other of sai elements being a nickel-iron alloy having a nickel content. of from substantially 38% to 45%.

9. A-thermostatic element comprising two cooperating metals having different coefiicients of expansion, one of said metals being a ferrous alloy containing nickel and manganese, and the other metal being a ferrous alloy containing 38% of nickel.

10. A thermostatic element comprising two cooperating metals having difierent coeificients of expansion, one of said metals being a ferrous alloy containing nickel and manganese, and the other metal being a ferrous alloy, containing nickel not in excess of 45%..

11. A thermostatic element comprisin two cooperating metal elements, one of sai elements being a 'ferrous alloy having a nickel content of from 38 to 45%, the other elen'ient being a ferrous alloy containing manganese and nickel insuch proportions that the percent amount of manganese plus substantially two and one-half times the percent amount of nickel is not less than substantially thirty percent of alloy aggreate. b 12. A thermostatic element comprising two cooperating metal elements, the low expansion element being a ferrous alloy containing substantially 38% nickel, and the high expansion element being-a ferrous alloy containing substantially ten percent of manganese and ten percent of nickel.

In testimony whereof, I have hereunto subscribed my name this 21st day of December, 1926.

HOWARD soo'rr. v

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